An international standard video coding method such as “MPEG-4 AVC/H.264” (referred to as “AVC” from now on) disclosed in Non-Patent Document 1 divides an image into blocks with an N×N pixel size and performs orthogonal transform such as a DCT (Discrete Cosine Transform), quantization and entropy coding of a predictive differential signal with the N×N pixel size, which is obtained by executing intraframe/interframe predictions on a block basis.
When executing predictive coding within a frame, the AVC acquires a differential signal by performing a prediction using pixels of adjacent blocks after the coding. As modes of the prediction, the total of nine modes is prepared which include an average prediction and which execute prediction from eight predictive directions.
When coding a moving image with a high resolution beyond a resolution (1920×1080) handled by a current HDTV (High Definition TV) by a conventional coding method, a method is employed which divides a picture and codes them in parallel to reduce a circuit size involved in an increase of arithmetic operations (see Patent Document 1, for example).
For example, when coding a moving image with 4096×2160 pixels, the coding is performed on a separate picture by separate picture basis with 2048×1080 pixels after quartering the single picture.
In this case, if the coding is carried out without cooperation in allocating a code amount among the separate pictures, differences in image quality can occur among the individual separate pictures. Accordingly, combining the separate pictures into a single picture will bring about unnatural deterioration in the image quality at boundaries.
To prevent such image quality deterioration, the following Patent Document 2 discloses a system which includes a unit for calculating for each separate picture a generated code amount and distortion characteristic as post processing of the coding and for storing the generated code amount and the distortion characteristic, and which determines the allocation of the code amount by estimating the code amounts of succeeding separate pictures by referring to the code amounts-distortion characteristics of the preceding separate pictures when coding the following picture.
As another method of coding a moving image with a resolution beyond the HDTV, Patent Document 2 discloses a system which produces two separate images by dividing an original image each alternate pixel on a block basis with an N×N pixel size, and which predicts a second separate image from a first separate image, followed by performing variable length coding of a differential signal.